1. Field of the Invention
The present invention relates to a sensor chip (semiconductor component for sensors) used for sensors for measuring pressure, acceleration, flow rate, temperature and the like, manufacturing method of the sensor chip and a laminated wafer used for manufacturing the sensor chip.
2. Description of Related Art
Japanese Patent Application Laid-Open No. Hei 8-235387 discloses a sensor chip used, for example, for electro-capacitance type pressure sensor.
The chip has a laminated structure where an electrode layer 200 is sandwiched between two glass substrates 201 and 202. As shown in FIG. 15, the electrode layer 200 is composed of a conductive silicon substrate and has a thick portion 200B around thin diaphragm 200A. The first glass substrate 201 and the second glass substrate 202 is bonded to the peripheral thick portion 200B. A predetermined gap is respectively formed between the respective glasses 201, 202 and the diaphragm 200A because the diaphragm 200A is thin relatively to the thick portion 200B.
When pressure is applied from a pressure inlet (not shown) provided to the second glass substrate 202 in the chip, the diaphragm 200A bends toward the first glass substrate 201 by the pressure from the second glass substrate 202. An electrode (not shown) is disposed on the first glass substrate 201 opposing the diaphragm 200A and electro-capacitance between the electrode and the diaphragm 200A changes when the diaphragm 200A bends. The pressure can be measured by electrically processing the change in the electro-capacitance.
For conducting such electric processing, respective signal receiving portions 203 and 204 for taking out electric potential of the electrodes (usually provided in plural) disposed on the first glass substrate 201 through a through-hole and another signal receiving portion 205 for taking out electric potential of the diaphragm 200A through the side of the chip are provided on a surface of the first glass substrate 201 (remote from the electrode layer 200). The signal receiving portions 203 to 205 and an outside circuit substrate for signal-processing are wired by wire-bonding etc. In the signal receiving portions 203 to 205, the signal receiving portion 205 for the diaphragm 200A has a terminal 205A provided in advance on the first glass substrate 201 and a continuous conductive layer 205B connecting the terminal 205A and an end of the thick portion 200B of the silicon substrate exposed on a side of the sensor chip. The conductive layer 205B is formed by vapor deposition, thermal spraying etc.
However, since the conductive layer 205B of the signal receiving portion 205 stretches to a lower end (a periphery of the second glass substrate 202 remote from the diaphragm 200A) of the sensor chip, the circuit substrate touches the conductive layer 205B when the chip is mounted to the circuit substrate, thereby causing possible electric failure such as noise pickup.
For overcoming above disadvantage, some special jig may be used for vapor deposition to prevent the conductive layer 205B from stretching to the lower end of the lower glass 201.
However, the structure of the jigs can be too complicated in the above arrangement, thereby making the attachment of the chip difficult. Additionally, since the small chip has to be carefully handled by a pair of tweezers and the like and the chips are collectively produced from a single wafer by a order of some hundreds pieces when the chip is attached to the jig, enormous time is necessary for attaching all the chips.
In order to cope with the electric failure and the disadvantage in productivity according to the structure shown in FIG. 15, another sensor chip is proposed, in which the thick portion 200B of the silicon substrate is exposed by a cut 206 as shown in FIG. 16 and the signal of the diaphragm 200A is directly taken out therefrom.
Such sensor chip can be manufactured by following steps of: drilling an opening of circular shape, for example, to the first glass substrate 201 in advance; forming the laminated wafer for sensor chip by laminating the first glass substrate 201 to the silicon substrate; and cutting the wafer at the position crossing the opening. According to the sensor chip, since the upper side of the silicon substrate exposed by the cut 206 is used as the signal receiving portion, the signal receiving portion is not required to be provided around the side of the chip, thereby making the vapor deposition on the side of the chip (cut surface exposed by cutting the wafer) unnecessary. Accordingly, when the signal receiving portion is formed, the vapor deposition can be done in the state of the wafer, i.e. without being cut into respective chips for forming the signal receiving portion, thereby greatly facilitating the attachment of the jigs and the like in vapor depositing step.
However, since the surface of the electrode layer 200 of the sensor chip exposed by the cut 206 forms a signal receiving portion as shown in FIG. 16, the size of the sensor chip increases. In other words, the surface of the electrode layer 200 exposed by the cut 206 has to be of a certain size for bonding and the like. However, the thick portion 200B used for the signal receiving portion also works for bonding the respective glass substrate 201 and 202 on the periphery of the diaphragm 200A. Accordingly, it is difficult to secure an area for the signal receiving portion to ensure the bonding strength and the electrode has to be extended to the outside. The above disadvantage is especially prominent in making a square diaphragm in line with the ordinarily square glass substrates 201 and 202, thereby eliminating useless area to increase area utilization efficiency for improving responsivity.
On the other hand, for overcoming the size-increase problem in the sensor chip shown in FIG. 16, though the electrode layer 200 is exposed by the cut 206, the signal receiving portion may be formed on the surface of the first glass substrate 201 as in FIG. 15, thereby connecting respective portions by the conductive layer 205B formed by vapor deposition etc.
However, following disadvantage occur in the above arrangement.
First, since the opening based on which the cut 206 is formed, is desirably formed as small as possible in forming the conductive layer 205B, it is difficult to conduct vapor deposition to the opening on the wafer, so that sufficient conductive layer 205B is not formed toward the bottom. Especially, the conductive layer 205B is likely to be discontinued at a corner of the bottom surface, as shown in FIG. 17.
Further, a break or a roll is likely to be generated to the edge portion around the opening 207 for the cut 206 previously formed on the first glass substrate 201. In this case, the aforesaid discontinuation of the conductive layer 205B is more likely to be caused since the break etc. forms concave when the first glass substrate 201 is laminated to the electrode layer 200.
In addition, the aforesaid conventional sensor chip has a disadvantage accompanied by anodic bonding electrode as well as the above-described disadvantage of signal receiving portion.
In the conventional sensor chip, a plurality of layers such as glass substrates and silicon substrates are laminated and often bonded by the anodic bonding. The anodic bonding is a bonding technique, in which a high electric voltage is applied to, for example, the fuirt glass substrate 201 and the electrode layer 200 under high temperature to bond them. In some cases, the plurality of layers is collectively anodic-bonded.
For conducting the anodic-bonding, an anodic-bonding electrode 208 is formed on the surface of the first glass substrate 201 in the sensor chip shown in FIG. 15.
The anodic-bonding is conducted in an area of the thick portion 200B where the first glass substrate 201 and the electrode layer 200 touches. The anodic-bonding electrode 208 has an approximately identical configuration as a profile of the diaphragm 200A for the anodic-bonding.
This is because the bonding strength increases as getting close to the anodic-bonding electrode 208 and the bonding strength is necessary to a portion of the thick portion 200B most adjacent to the diaphragm 200A. However, a partial curved detour in view of the position of other electrodes and through-holes and a partial cut for passing the conductor is provided as necessary.
Such anodic-bonding electrode 208 is not removed and is retained on the first glass substrate 201 even after being manufactured as a sensor chip.
However, following disadvantages can occur when the anodic-bonding electrode 208 is retained.
First, in the sensor chip manufactured by the aforesaid anodic-bonding, a confirmation process is necessary for checking whether there is bonding failure (insufficient bonding, mixing foreign substance etc.). The confirmation work is done by visually checking the anodic-bonding surface looking through the first glass substrate 201. Accordingly, when the anodic-bonding electrode 208 is retained on the first glass substrate 201, the anodic-bonding electrode 208 can be an obstacle for the visual confirmation, so that the anodic-bonded surface has to be observed in a multiple of directions obliquely, thereby largely deteriorating work efficiency. Further, since the anodic-bonding electrode 208 visually blocks, using automation machinery is impossible for improving work efficiency.
Second, when the anodic-bonding electrode 208 is retained on the sensor chip, a part of the anodic-bonding electrode 208 can be peeled off to cause contamination problem and removing work can be troublesome for marketing as a pressure sensor. This is thought to be because sodium ion in the first glass substrate 201 concentrates around the anodic-bonding electrode 208 by applying a minus-electric voltage in anodic bonding process so that the sodium ion is educed to deteriorate the electrode base member, making it easy to be peeled off even when the anodic bonding electrode 208 is firmly formed, which is an inevitable problem as long as the anodic-bonding electrode 208 is retained.